The image above is the mushroom cloud about 15-20 secs after the blast that is now called the Halifax Explosion.
The explosion occurred on Thursday, December 6, 1917 (during WWI), when the city of Halifax, Nova Scotia, Canada, was devastated by the huge detonation of wartime explosives occurred when two ships - the SS Mont-Blanc, a French cargo ship and the Norwegian SS Imo - collided in “The Narrows” section of the Halifax Harbour.
About 2,000 people were killed by debris, fires, or collapsed buildings and it is estimated that over 9,000 people were injured. This is still the world’s largest man-made accidental explosion.
Photograph of rescue workers in downtown Halifax searching for survivors following the huge blast that shattered homes killing over 2,000 people and injured about 9,000.